1. Field of the Invention
The present invention relates generally to a suspension rubber bushing adapted to be installed in a suspension assembly to exhibit desired damping effect, and more particularly to a suspension rubber bushing of vertical mounted type that is used with its bushing axis oriented vertically.
2. Description of the Related Art
Conventionally, a suspension rubber bushing (hereinafter simply referred to as a “rubber bushing”) may be disposed at a linkage point between a vehicle body and a control arm in an automobile suspension, in order to ensure turning of the control arm, and to provide vibration damping between the control arm and vehicle body, so that the vehicle body and suspension are elastically linked via the rubber bushing.
FIG. 6 illustrates an example of such a suspension system. In the drawings, 200 denotes a tire, and 202 a control aim having fixing bores 204 disposed at bifurcated front and rear end portions thereof, with a rubber bushing 206 secured press-fit into one of the fixing bores 204 (i.e., the front one). A rubber bushing 206 has an outer metallic sleeve 210, an inner metallic sleeve 212, and a rubber elastic body 214 interposed therebetween, elastically connecting the inner and outer sleeves 210, 212. This rubber bushing 206 is press fitted at its outer sleeve 210 into the fixing bore 204, and at its inner sleeve 212 is linked to the vehicle body. It is noted that the rubber bushing 206 is employed in a horizontal mounting in which a bushing axis is oriented on the horizontal (front-back orientation).
In contrast to the aforesaid conventional arrangement, there has in recent years been research into the use of a vertical mount rubber bushing 208 in which the bushing axis is oriented vertically, as the rubber bushing on the other fixing bore 204 (i.e., the back one). In the case of the vertical mount rubber bushing 208, both of the outer and inner sleeves 210, 212 are oriented vertically, the two being elastically connected by means of the rubber elastic body 214. The fixing bore 204 is also oriented vertically so that the rubber bushing 208 is press fitted therein.
In the present vertical mount rubber bushing 208, the body or main portion of the rubber elastic body 214 having a large thickness is oriented to extend so as to connect the outer sleeve 210 and the inner sleeve 212 in approximately the vehicle front-back direction, and has a high spring constant in the same direction, while having a soft spring constant in approximately the vertical left-right direction at a right angle thereto. This arrangement provides good absorption of shock and vibration when the tire 200 rides over a bump during driving.
When the tire 200 rises over a bump, the control arm 202 attempts to undergo rotational motion in the direction indicated by arrow P in FIG. 6. Since the rubber bushing 208 has soft spring characteristics in the direction of input of force applied at this time, and readily deforms in response thereto, thereby providing good moderation of the shock applied to the tire 200, and effectively damping transmission of shock to the vehicle body.
Where the vertical mount rubber bushing 208 is used at one end of the control arm 202, the vertical mount rubber bushing 208 is likely to suffer from a high level of prizing force when the control arm 202, in association with up and down motion of the tire 200, rotates up and down about a supporting portion, which is the linkage point of the control arm 202 to the vehicle body by means of the rubber bushing 206, 208. In this regards, meant by “prizing force” is force oriented so as to tilt the inner sleeve 212 relative to the outer sleeve 210.
That is, if a rubber bushing 216 of a conventional horizontal mount type as shown in FIG. 7, for example, is used without modification in a vertical mount as a vertical mount rubber bushing of the aforesaid type, the problem becomes significant. Namely, when subjected to prizing force, the inner sleeve 212 tilts appreciably at an angle θ with respect to the outer sleeve 210, producing a high level of strain in the rubber elastic body 214 at this time. This results in a likelihood of earlier fatigue of the rubber bushing 216 with repeated input of prizing force.
As one means of solution of this problem, it would be conceivable to affix the rubber elastic body to the axially center portion of the inner sleeve, and to form depressed spaces situated to either axial side of this center portion and between the inner sleeve and the rubber elastic body, as disclosed in the following Patent Documents 1 and 2.
[Patent Document 1]                JP-B-2538464        
[Patent Document 2]                JP-A-2001-271865        
However, where the rubber elastic body is shaped to have an approximately constant cross sectional shape over its entire circumference, the rubber bushing 208 is able to achieve a high level of endurance against applied force based on rotational motion of the control arm 202 in the vertical direction in FIG. 6, for example, but fails to achieve an intended function due to its spring constant that becomes small in the approximately front-back direction in FIG. 6. Also, the rubber bushing 208 suffers from appreciable deformation of rubber elastic body 214 when subjected to load in this front-back direction, so that endurance life in this direction declines.